This invention relates to the removal of cataracts and to equipment for such removal.
In one prior art surgical technique for the removal of cataracts: (1) an incision is made along the superior corneal margin from about 10 to 2 o'clock (12 o'clock is the location closest to the top of the head of the patient) approximately 10 mm in chord length; (2) a large part of the anterior capsule is removed; (3) the nucleus is expressed out of the eye; (4) the cortex is removed by a process of irrigation and aspiration; and (5) the lens is replaced with a lens implant. The anterior chamber is maintained substantially formed during the operation by means of a continuous inflow of irrigating solution in an amount ranging from 50 to 500 ml.
In one other prior art technique designed to improve the above in substantially reducing the amount of irrigating fluid to no more than 1-3 milliliters: (1) an incision is made along the superior margin of the cornea from 10 to 2 o'clock; (2) the anterior chamber is filled with viscoelastic compound to maintain its usual form; (3) a horizontal incision in the anterior capsular wall is made at a location away from the center of the capsular bag; (4) the nucleus is removed with a vectis; and (5) about 0.1 milliliter of liquid is introduced into the capsular bag to separate the capsular walls. A wedge of the cortex is engaged in the aspiration port of a cannula and peeled toward the center and then aspirated to remove it behind the anterior capsule within the capsular cavity. This process is repeated so that the layers of the cortex are peeled and then aspirated inwardly through the cannula layer by layer until the intact capsular bag (except for the horizontal incision) is completely empty and clean. This technique of removing the cataract is disclosed by Anis, Aziz Y. "Illustrated Step-by-Step Description of the Anis Dry Extra Capsular Cataract Extraction Technique With In-the-Bag Lens Implementation"; Seminars in Opthalmology, v. 1, N. 2 (Jun.), 1986, pp. 113-129.
This technique has the disadvantage of requiring a larger incision than desirable. Two prior art types of instruments which aid in the fragmentation and aspiration of the lens nucleus to permit extraction through a small incision are disclosed in U.S. Pat. No. 3,589,363 to Anton Banko, et al.; U.S. Pat. No. 3,902,495 to Steven N. Weiss; U.S. Pat. No. 3,693,613 to Charles Kelman, et al.; and U.S. Pat. No. 4,041,947 to Steven N. Weiss, et al. This instrument is intended in the prior art to fragment a lens nucleus using ultrasonic sound to aid the irrigation/aspiration of the lens.
The prior art use of this instrument to fragment the lens with ultrasonic sound, a procedure called phako emulsification, has several disadvantages, such as: (1) the instrument is larger than desirable and thus may cause damage to the cornea at the site of entry; (2) the prior art use of the instrument imparts so much energy into the eye as to increase the possibility of damage to the structure of the anterior segment; (3) the prior art use of the instrument uses much fluid particularly during the nucleus fragmentation and during the irrigation and aspiration process of the cortex, thus increasing the possibility of damage to the corneal endothelium, sometimes to the extent of reducing the visibility of the surgeon during the operation because of corneal stromal edema and fluid turbulence in the anterior chamber; (4) the instrument increases the amount of agitation within the eye from the force of the ultrasonic vibration, thus increasing the possibility of damage to the eye structure by bombardment with nuclear fragments flying from the point of impact of the instrument with the nucleus; and (5) turbulence of the inflowing fluid can wash away a large number of non-regenerable vital cells of the corneal endothelium.